150 BIOLOGICAL PROBLEMS 



About this time, too, as spraying requirements be- 

 came more general, power-driven spraying outfits 

 were designed for spraying over large areas from 

 a central mixing station. These plants, besides the 

 necessary engine and pumps and mixing plant, 

 required the laying of some miles of piping and 

 involved the outlay of some thousands of pounds. 



These outfits, of course, required the use of still 

 stronger pumps, as a pressure of 200 to 300 pounds 

 was necessary to ensure the requisite pressure of 

 about 100 pounds at the point of delivery, the 

 nozzle. 



A further development occurred a little later, when 

 the horse-drawn, hop-washing machines were fitted 

 with motor engines for driving the pumps, whilst one 

 or two horses drew the machine along. 



These machines have now been introduced for use 

 in young orchards, the waste of spraying mixture 

 between the trees being more than compensated for 

 by the great saving of time and the resulting ability 

 of the grower to combat quickly any attack of pest. 



One of the principal developments in spraying has, 

 however, been in the nozzle. In the early days the 

 usual thing was to drill a fine hole or two in a pipe or 

 nozzle end, and this was constantly choking up; in 

 fruit-tree spraying a very much finer spray was 

 required, while it was necessary, owing to the varying 

 kinds of spray fluids to be used, to have a compara- 

 tively large aperture in the nozzle, so that everything 

 which would pass the strainer would come out of the 

 nozzle. Nozzles were consequently constructed so as 

 to impart a rotary motion to the fluid and with a 

 simple means for controlling the proportion of rotary 

 to direct action, nozzles were produced which could 

 be set to give any character of spray to suit all kinds 

 of requirements. The nozzles now produced are as 



